Piston for internal combustion engine, internal combustion engine including this piston, and manufacturing method of this piston

Abstract

There is provided a piston for an internal combustion engine, the piston including: a heat-shielding film provided to an upper surface of a land part of the piston, the heat-shielding film having a lower thermal conductivity than a piston base material and having a lower heat capacity per unit volume than the piston base material; and a first heat-retaining film provided to a side surface of the land part, the first heat-retaining film having a lower thermal conductivity than the piston base material and having a higher heat capacity per unit volume than the heat-shielding film.

What is claimed is: 
     
       1. A piston for an internal combustion engine, the piston comprising:
 a heat-shielding film provided to an upper surface of a land part of the piston, the heat-shielding film having a lower thermal conductivity than a piston base material and having a lower heat capacity per unit volume than the piston base material; and 
 a first heat-retaining film provided to a side surface of the land part, the first heat-retaining film having a lower thermal conductivity than the piston base material and having a higher heat capacity per unit volume than the heat-shielding film, 
 wherein the heat-shielding film is an anodized film, 
 wherein the heat-shielding firm is not provided to the side surface of the land part, 
 wherein the first heat-retaining film is provided to a part of a side surface of a top land, and the top land is a portion of the land part further on the upper side than a groove in which a top ring is fitted, and 
 wherein a surface roughness of the first heat-retaining film is lower than a surface roughness of the heat-shielding film. 
 
     
     
       2. The piston according to  claim 1 , wherein
 the side surface of the top land located on the side of the upper surface of the land part has a higher heat-retaining effect than the side surface of the top land located on the side of a lower surface of the land part. 
 
     
     
       3. The piston according to  claim 1 , wherein
 the piston base material is exposed in a portion of the side surface of the land part further on the lower side than the groove. 
 
     
     
       4. The piston according to  claim 1 , wherein the first heat-retaining film is a hard alumite having a lower porosity than the heat-shielding film resulting in the higher heat capacity per unit volume than the heat-shielding film. 
     
     
       5. A piston for an internal combustion engine, the piston comprising:
 a heat-shielding film provided to an upper surface of a land part of the piston, the heat-shielding film having a lower thermal conductivity than a piston base material and having a lower heat capacity per unit volume than the piston base material; and 
 a first heat-retaining film provided to a side surface of the land part, the first heat-retaining film having a lower thermal conductivity than the piston base material and having a higher heat capacity per unit volume than the heat-shielding film, 
 
       wherein
 a second heat-retaining film is provided to an inner wall surface of a cylinder that houses the piston, 
 the second heat-retaining film is provided at such a position that the second heat-retaining film faces the side surface of the land part when the piston is located at a bottom dead point, and 
 the second heat-retaining film has a heat capacity per unit volume lower than that of the piston base material and higher than that of the heat-shielding film. 
 
     
     
       6. A manufacturing method of a piston for an internal combustion engine, the piston including:
 a heat-shielding film provided to an upper surface of a land part of the piston, the heat-shielding film having a lower thermal conductivity than a piston base material and having a lower heat capacity per unit volume than the piston base material; and 
 a first heat-retaining film provided to a side surface of the land part, the first heat-retaining film having a lower thermal conductivity than the piston base material and having a higher heat capacity per unit volume than the heat-shielding film, the manufacturing method comprising: 
 forming the heat-shielding film on the upper surface of the land part by anodizing the piston base material; and 
 after forming the heat-shielding film, forming the first heat-retaining film on the side surface of the land part by forming a film of an insulating material, the insulating material having a lower thermal conductivity than the piston base material and having a higher heat capacity per unit volume than the heat-shielding film.